Process for sweetening naphthas



United States Patent() Mice "PROCESS FOR SWEETENING NPHTHS Georges G. Lukk, Cameron H. Caesar, and Stephen Ilnyckyj, Westlield, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Application November 15, 1952, Serial No. 320,706

Claims. (Cl. 208-203) The present invention is concerned with an improved sweetening process. The invention is more particularly concerned with the conversion of mercaptan compounds, particularly those mercaptan compounds which-have heretofore been relatively diicult to remove from hydrocarbon fractions, especially from those fractions Vboiling in the motor fuel, kerosene, diesel cil and heating oil boiling ranges. In accordance with the Vpresent invention, a feed hydrocarbon oil characterized by containing mercaptan compounds is contacted with an Ioxygen-`contain ing gas and a treating agent comprising activated carbon impregnated with a critical amount of caustic.

lt Yis -well knownin the art to treat petroleum Voils by various procedures in order to vrenlove .or `convert objectionable compounds to less objectionable materials, as for example, it is known to .treat .petroleum fractions boiling in the motor Ifuel boiling range and in the general range below about 700 F. with various Ychemical reagents Asuch as sodium or potassium hydroxide solutions. Also it is known that weakly acidic materials, such as mercaptans, are reactive to various degrees with basic materials. Thus, one method for the removal of mercaptans from hydrocarbon streams has been to treat the streams with a reagent which is insoluble in the hydrocarbon stream ibut which contains alkali .type of material which reacts with mercaptans. Such treating ,reagents have normally been aqueous solutions. The :reaction product is a basic salt of the mercaptan. Normally such salts exhibit some solubility in the aqueous phase, this solubility decreasing as the molecular weight or branchiness of the hydrocarbon structure of the mercaptan increases.

The art has generally Vbeen recognized in the treating of hydrocarbon streams with aqueous solutions such as strong or weak caustic in la continuous type process, that the equilibrium is generally unfavorable for mercaptan extraction. Therefore, caustic solutions when they are spent only to a small extent in mercaptide salts will not give any further reduction in mercaptan content despite the fact that these treating solutions have a large residual free-caustic content. The art has also recognized that the efliciency of the spent caustic can be partially -or fully restored by regeneration VIof lthese solutions. The -regeneration normally consists of removal of a part or all of the mercaptide salts by means of hydrolysis and vapor ization or by oxidation.

One method is to employ steam regeneration for the revivitication of caustic solution spent in ltmei'captan yremoval from hydrocarbon streams. The stea'm'regeneration is normally carried 4out in a packed toweror a tow er provided with bubble plates 'or pierced'type tray plate f the steam vapors and taken overhead. The regenerator also serves 'as-a means of adjusting the gravity ofi-the caustic solution, which has been shown to be The regenerated caustic is withdrawn from the bottom 2,908,637 Patented Oct. 13, 1.959

`of the regeneration tower and reused in the extraction stage of the system wherein the caustic contactsthe hydrocarbon stream :through suitable mixing devices for further .extraction of mercaptans by the Samecaustic.

It has also been suggested that Va treating agent comprising carbon and Vcaustic be utilized for the removal `of ymercaptan compounds from :an oil by converting `the .mercaptan to corresponding relatively harmless mercaptides and adsorption rof the latter on the carbon. It .has now been discovered that the mercaptides in vthe causticon-.carbon system can Vbe `readily oxidized to disulphides. This increases greatly the amount of feed which `can be sweetened by a batch of caustic impregnated activated carbon, provided that an oxidizing agent, eg., oxygen is dissolved in the feed. It has been further vdiscovered that `if va critical ratio of carbon .to caustic is employed, unexpected desirable results lare secured both with respect `to the extent of `conversion of mercaptans to `disuliides and with respect to `the .catalyst life.

The process of the present invention may be more fully understood by reference to the drawing illustrating an embodiment o-f the same.

Referring specifically to the drawing, a light virgin naphtha feed oil boiling in ythe range from about 100 F. to 300 F. is introduced into the system by means of line l. The oil is passed through a sand tlter 2 wherein any water is segregated from the oil and removed Vby means -of line 3. The oil is removed 'from lil-ter 2 by means of line 4 `and `mixed with an oxygen-containing gas as for example air, which is introduced into the system by means of line 5. Theoil is then passed alternately through reactors 7 and 8 `wherein 'the `same is contacted with activated carbon impregnated with caustic soda. The treating agent xis prepared preferably by mixing water which is introduced into the system by means of line 9 with sodium hydroxide, preferably in a concentration of about 50 B. which is introduced into the system by means of line 10. The aqueous caustic is passed to a mixer 11 where in the same is mixed with activated carbon which is introduced into the system by means of line 12. The finished catalyst is mixed in a slurry :drum type mixer 13 with naphtha 4from line 15 and passed to the respective reactors A'7 or 8 by means of line 14. Treated .oil is removed from the reactors 7 and 8 by lines 16 and 17 respectively. The treated product is passed `to a product storage zone 18 wherein the airis removed by means of line 19.

While the operation has `been 4described wherein naphtha is percolated through a xed bed of activated carbon impregnated with caustic, it is to be understood that a fluidized bed or a slurry type operation may be utilized. In accordance with the present invention air or lother oxygen-containing ,gas is introduced into the naphtha stream prior to percolating the feed through the impregnated activated carbon in order to supply the oxygen required for the oxidation reaction in accordance with the following:

consists of carbon impregnated with an aqueous solution of Van alkali metal hydroxide. The amount of this solution, should be 50% or less than the maximum amount -that `can be taken up by Ithe carbon. The ratio of the hydroxide to water should be such, that a solution rather than a solid will result at the operating temperature. For

example, the weight of sodium hydroxide should not exlceed the weight of the water. In the case of potassium hydroxide a higher concentration of KOH to water can 'be used. Whenemploying a catalyst of these critical 'ratios, a high degree of conversion is secured and a high fcatalyst life.

'The catalyst of the present invention may be prepared leither by (1) direct mixing of the components or by (2) --soaking the carbon in dilute caustic followed by removal fof the excess Water by drying. An application of the rst method is illustrated in the attached drawing. Activated carbon and a solution of caustic in water are introfduced simultaneously into a mechanical mixer, e.g. of the concrete mixing type. lf the components are introduced separately the carbon is first added to the mixer `followed by the caustic solution. The proportions of 'the three components are selected in accordance with -the desired final catalyst composition. The optimum addi- Vtion rates of the components (or of the caustic solution) 'will depend upon the eiciency of the mixing device. Mixing times of 10 to 15 minutes are adequate.

The alternative method of soaking and drying appears 'to be particularly suited for catalyst preparation or regeneration in situ.

The process of the present invention may be more fully understood by the following examples illustrating the :same.

EXAMPLE 1 A number of operations were conducted wherein the 'treating agent comprised activated carbon impregnated with caustic; activated carbon alone and caustic alone.

'The results of these operations are shown in the following table:

Table l INDIVIDUAL ACTION OF COMPONENTS OF CAUSTIC-ON- ACTIVATED-CARBON CATALYST Feedstock-Naphtha of 100-250 F. Boiling range, 16 Cu No. Air to feed ratio-U3.

EFFECT OF AIR T FEEI l From the above it is apparent that unexpected results are secured utilizing activated carbon in conjunction with caustic and air.

EXAMPLE 2 A number of operations were conducted wherein catalysts prepared by different procedures were utilized. The results of these operations are given in the following table:

Table Il EFFECT OF METHOD OF CATALYST PREPARATION gAPg'lTOSNWEETENING WITH CAUSTIC ON ACTIVATED Feedstock-Naphtha of F. to 250 F. Boiling range, 15 Cu No. Catalysts-56% dry carbon, 12% NaOH, 32% water.

Air to feed ratio-U4.

Feed rate-8 WJW. (catalyst)/hr.

Catalyst Preparation- Direct Mixing of Soaking and Drying Components Converted S Converted S Bbls. Feed/Lb. of Cu N o. of as equivalent Cu No. of as equivalent Catalyst Product percent of Product percent of N aOH of Catalyst 1 Doctor 44 Pass.

From the above it is apparent that while the soaked and dried catalyst exhibits a higher activity in the early part of the sweentening operation, the catalyst prepared by ydirect mixing shows superior activity maintenance.

EXAMPLE 3 A number of operations were conducted wherein the amount of air utilized was varied. The results of these operations are shown in the following table:

Table III RATIO ON SWEETENING WITH CAUSTIC ON CTIVATED CARBON Feedstock-Naphtha of 100 F. to 250 F. Boiling range, 15 Cu Noz Catalysts-56% dry carbon, 12% NaOH, 32% water, prepared by mixlng. Feed Bate-8 \v./w. (catalyst)lhr.

Air to feed vol.

ratio 1/3 1/1.5 1/0.7

Converted Converted Converted S as as as Bbls. feed per Cu 1go. of equivaltenft Cu 1go. gf equivalteng: Cu Ndo. 2f equivalteng; 1b. f t l t ro uct ercen o ro uc percen o pro uc pcrcen o o ca a ys p IlaOH of p NaOH of NaOH of catalyst catalyst catalyst Doctor 88 88 Doctor 88 Pass Pass 0.5 172 172 P 175 0.5 257 257 D.P- 263 2.0- 333 342 0.5 348 2.5 406 424 2.0 424 3.0 475 500 9.5 456 Umw EXAMPLE 4 A number of operations were conducted wherein the ratlo of carbon to caustic was varied. The results of these operations are given in the following table:

Table IV 6 4. A process as defined by claim 1 wherein said oil is contacted with said catalyst in the presence of from 1 to 6 times the amount of oxygen theoretically required for the conversion of mercaptans into disuldes.

EFFECT OF CATALYST COMPOSITION ON SWEgl'NG 0F NAPHTHA WITH CAUSTIO ON ACTIVATED [Variations of moisture content at O to NaOH ratio of 61: 13 and of carbon content at NaOH to H2O ratio of 13:26]

Feedstock-Naphtha 100 F. to 325 F.E.P., 16 Cu No. Catalysts-Prepared by soaking and drying carbon, /100 mesh. Feed rate-125 W./W. (of carbon) Ihr.

Air to feed ratio-2/3.

Catalyst composition (dry base/NaOH/HgO) oper 1 2 a 4 5 5 7 s 9 10 11 BblsJlb. of Percent RSE converted carbon 0.25 s1 s2 96 97 9s 91 77 31 4o s2 77 0.5 55 74 92 94 95 se 66 25 28 71 6s 1.o 54 55 s6 ss so 78 52 1s 2o 52 5s 2.0 42 55 76 79 so e3 40 51 47 4.0 35 43 65 69 62 44 2s a9 34 8.0--- 29 31 54 5s 2s 20 2s 26 12.0 55

l Carbon saturated with caustic solution.

From the above it is apparent that a catalyst which 5. A process for the conversion of mercaptans in a comprises to 62 parts by weight of 20 to 100 mesh 30 naphtha into disuldes which comprises contacting said carbon, 11 to 14 parts by weight of alkali metal hydroxnaphtha with from 1 to 6 times the amount of oxygen ide and from 33 to 25 parts by weight of water is superior. theoretically necessary for conversion of the mercaptans With ner carbon of the same type better results are therein into disuliides and with a catalyst consisting essenobtained if the concentration of the solution is increased. tially of from 55 to 62 parts by weight of 20 to 100 What is claimed is: 35 mesh activated carbon, 11 to 14 parts by weight of 1. A process for converting mercaptans contained in sodium hydroxide and 25 to 33 parts by weight of water. a hydrocarbon oil boiling in the motor fuel boiling range into disuliides which comprises contacting said oil in the References Cited 111 the 111e 0f 1111s 132111711t presence of an oxygen-containing gas with a catalyst con- UNITED STATES PATENTS sisting essentially of 20 to 100 mesh activated carbon 40 having an aqueous alkali metal hydroxide solution ad- 1,098,764 RlChtel 11111@ 2, 1914 sorbed thereon; said catalyst containing from 55 to 6 2 1,890,516 Lachmall DCC- 13, 1932 parts by weight of carbon, from 11 to 14 parts by weight 1,955,607 Rees et al- API'- 17, 1934 of alkali `metal hydroxide and from 25 to 33 parts by 1,957,794 M Offell et 21- May 8, 1934 Weight of Water. 45 2,577,824 Stine D60. 11,

2. A process as defined by claim 1 wherein said alkali metal hydroxide is sodium hydroxide.

3. A process as defined by claim 1 wherein said oxygen-containing gas is air.

OTHER REFERENCES Voreck et al.: Petroleum Rener, vol. 30, No. 3, pages 126-129. 

1. A PROCESS FOR CONVERTING MERCAPTANS CONTAINED IN A HYDROCARBON OIL BOILING IN THE MOTOR FUEL BOILING RANGE INTO DISULFIDES WHICH COMPRISES CONTACTING SAID OIL IN THE PRESENCE OF AN OXYGEN-CONTAINING GAS WITH A CARALYST CONSISTING ESSENTIALLY OF 20 TO 100 MESH ACTIVATED CARBON HAVING AN AQUEOUS ALKALI METAL HYDROXIDE SOLUTION ADSORBED THEREON; SAID CATALYST CONTAINING FROM 55 TO 62 PARTS BY WEIGHT OF CARBON, FROM 11 TO 14 PARTS BY WEIGHT FO ALKALI METAL HYDROXIDE AND FROM 25 TO 33 PARTS BY WEIGHT OF WATER. 